A personal computer is typically coupled to peripherals that serve as computer-user interfaces. Such peripherals may include a keyboard, a mouse, and a monitor. Typically standard cables connecting each peripheral are around four feet long. Because of the characteristics of the connecting cables and their interfaces, the cables do not provide a reliable peripheral connection when they are much longer than twenty feet.
There are situations where it is desirable to separate the computer from the peripherals at distances much greater than allowed by typical standard peripheral cables. The apparatus to extend the distance between a computer and peripherals is called an extender or an extension system. One such system, PC-Extender Plus is available from Cybex Computer Products of Huntsville, Ala. The PC-Extender Plus allows a keyboard, monitor, and mouse to be placed up to 600 feet away from the computer. An extender typically has two electronic boxes and several cables between the computer and the peripherals. As the demand for extenders increases, the need for more efficient use of cables has developed.
In existing extenders, standard coaxial cables, shielded cables, and unshielded cables serve as communication channels. In addition, custom cables have been developed to provide an improved communication channel for some extender systems. The cables connecting the computer to the peripherals may be confined in a binder or may be separate cables for each of the desired connections. The apparatus or electronic boxes connected to the ends of each cable serve as interfaces between the computer and the cable at one end and the peripherals and the cable at the other end.
A recently developed digital system for extending computer peripherals is described in U.S. application Ser. No. 08/971,223 filed on Nov. 15, 1997 still pending and is assigned to the assignee of the present invention and is hereby incorporated as a reference herein. One of the problems occurring in the recently developed system was the coupling of open collector circuits between the computer and peripherals in a way that was compatible with existing hardware and operationally transparent to a computer user. A similar problem occurs in analog extension systems and was solved as described in U.S. Pat. No. 5,587,824 issued to Asprey. In Asprey an arrangement of analog circuit elements is used to allow a long wire to appear as a short wire to open collector circuits. The recently developed system of application '223 provides a bidirectional data flow using a half duplex transmission method and placing peripheral bits in data packets. Because the recently developed digital system converts analog signals to digital signals, transmits the digital signals in packets, then converts the digital signals back to analog signals the invention of Asprey is not applicable.
Accordingly, it is the object of this invention to provide a means for coupling open circuit collector circuits in a manner that is transparent to the user and does not add significant cost to a digitally based extension product. To provide such a means requires the development of an algorithm, method, or apparatus within the framework of the recently developed system or other bidirectional data communication system. Such a solution should function as a virtual wire to the user and perform essentially as a short piece of wire typically used to couple open collector circuits.